Electronic dosing devices are utilized in particular in scientific and industrial laboratories with medical, molecular biological and pharmaceutical areas of application for dosing liquids. Electronic dosing devices have an electronic dosing drive for driving a plunger in a cylinder. In direct displacement systems, the dosing device is coupled with an exchangeable syringe. The electronic dosing drive drives a syringe plunger in a syringe cylinder of the syringe, through which the receiving of liquid into the syringe and the discharge of liquid from the syringe is controlled. In doing this, the syringe plunger comes into contact with the liquid. The discharge occurs preferably in multiple steps. The syringe is exchangeable in order to prevent carryovers when different liquids are dosed with the same dosing device.
In the case of air cushion systems, the electronic dosing device comprises, besides the dosing drive, a cylinder and a plunger that can be displaced therein and is coupled with the dosing drive. Furthermore, the dosing device has a seal seat for firmly clamping and sealing a pipette tip. A hole in the seal seat is connected to the cylinder via a channel. The pipette tip is a tube with a lower opening on the lower end and an upper opening on the upper end. By moving the plunger in the cylinder, air can be displaced through the upper opening in order to suck liquid into and expel liquid out of the pipette tip through the lower opening. In doing this, the plunger and cylinder do not come into contact with the liquid. The pipette tip can be exchanged after use.
The syringe and pipette tip are typically made of plastic.
Electronic manual dosing devices can be carried and operated by the user with only one hand. Direct displacement systems are also termed electronic dispensers or repeating pipettes. Air cushion systems are also termed pipettes. They are hereby semi-automated, since they must be positioned and operated by hand, wherein the (syringe) plunger is driven by an electric drive motor. Compared to dosing devices with manual drives, the high reproducibility and the precision, the user-friendliness and ergonomics as well as the multi-functionality are advantageous and enable dispensing, reverse pipetting, diluting, mixing and titrating.
Furthermore, electronic dosing devices are integrated into automated dosing systems (LHS=liquid handling stations) and automated laboratory systems (WS=work stations). These have a dosing tool and a robot arm for positioning the dosing tool. The robot arm is, for example, an XYZ transfer system. They enable quick and reproducible fully automated dosing via pipetting, dispensing or other dosing methods.
The electronic dispensers Multipette® E3/E3x comprise a housing with a first receiver for a syringe flange of a syringe cylinder of the syringe and a receiving body with a second receiver for a plunger rod end of the syringe plunger. Furthermore, the housing comprises an electronic dosing drive that comprises a spindle drive with a threaded spindle and a spindle nut, and an electric drive motor. The receiving body is firmly attached to one end of the threaded spindle and is guided in the longitudinal direction of the threaded spindle in the housing. The electric drive motor firmly arranged in the housing is coupled with the spindle nut. An electric control apparatus is connected to the electric drive motor, and an electrical power supply is connected to the electric drive motor and the electric control apparatus. The threaded spindle and spindle nut are made of metal.
The electronic pipettes Xplorer®/Xplorer® plus from Eppendorf AG have in the housing at least one cylinder with a plunger movable therein. Each cylinder is connected via a channel to a hole in an attachment for clamping on a pipette tip. These pipettes exist as single-channel pipettes with only one cylinder, one plunger movable therein and one attachment connected to the cylinder. They also exist as multi-channel pipettes with multiple cylinders, plungers movable therein and attachments connected to the cylinders. A threaded spindle is connected to the at least one plunger and is guided in the longitudinal direction in the housing. Otherwise, the electronic dosing drive of these electronic pipettes corresponds to that of the electronic dispensers.
A disadvantage is the complex manufacturing of the threaded spindle by means of highly precise lathes and finishing, for example by deburring. Furthermore, a hitting of the threaded spindle can occur if it protrudes farther out of the spindle nut with the non-guided end. The spindle drive is susceptible to corrosion. Corrosion increases the friction and therefore the wear as well as decreasing the dosing accuracy. The spindle drive requires lubricant, which binds dust, through which the wear is increased and the dosing accuracy is lowered. Overload can lead to plastic deformation which also lowers the precision of the spindle drive.
DE 10 53 883 A describes a threaded spindle made of sheet metal that is composed of two U-profile strips that are welded to each other on their longitudinal edges. The distance between the welding beads on both sides of the threaded spindle is smaller than the diameter of the thread core. This threaded spindle is suitable for simple jacks taken along by the driver, for work-holding devices on workbenches and joiner's benches, for example in joiner's and glazier's workshops, for screw clamps and other apparatuses for which the requirements on the spindle regarding the running characteristics are not too high.